Polyaxial bone anchoring device and instrument for use with the same

ABSTRACT

A bone anchoring device includes a receiving part with a rod receiving portion having a first end, a second end, a recess for the rod, an outer surface, and a first engagement structure on the outer surface that extends farther radially outwardly than other parts of the rod receiving portion, and a flexible head receiving portion for inserting and clamping the head. The bone anchoring device also includes a locking ring configured to be arranged around the head receiving portion for locking the head, the locking ring having an outer surface and a second engagement structure on the outer surface that extends farther radially outwardly than the outer surface of the rod receiving portion. The engagement structures are configured to be engaged by an instrument to move the locking ring from a locking position to a position where the inserted head is pivotable.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims the benefit of U.S. Provisional PatentApplication Ser. No. 62/196,739, filed Jul. 24, 2015, the contents ofwhich are hereby incorporated by reference in its entirety, and claimspriority from European Patent Application EP 15 178 383.4, filed Jul.24, 2015, the contents of which are hereby incorporated by reference inits entirety.

BACKGROUND

Field

The invention relates generally to a polyaxial bone anchoring device andan instrument for use with the device. More specifically, the boneanchoring device includes a receiving part for coupling a rod to a boneanchoring element, wherein the receiving part has a rod receivingportion for receiving the rod and a head receiving portion for clampinga head of the bone anchoring element, and a locking ring for locking thehead in the head receiving portion. The receiving part and the lockingring are configured to be movable relative to each other from a nonlocking position to a locking position, and vice versa, for example, byusing an instrument.

Description of Related Art

US 2011/0276098 A1 describes a polyaxial bone anchoring device includinga receiving part for receiving a rod for coupling the rod to a boneanchoring element, the receiving part including a rod receiving portionwith a channel for receiving a rod and a head receiving portion that isflexible for clamping a head of the bone anchoring element. A lockingring is configured to be positioned around the head receiving portion.The locking ring can assume a first position where the head receivingportion is expandable to facilitate insertion of the head and a secondposition in which the locking ring compresses the head receiving portionsuch that the head is held adjustably at a first angular positionrelative to the receiving part. Further, the locking ring can assume athird position in which the head is locked in the receiving part. Forlocking the head, a locking element is used that also locks the rod inthe rod receiving portion.

US 2013/0085536 A1 describes a polyaxial bone anchoring device includinga receiving part with a rod receiving portion and head receiving portionfor introducing and clamping of the head and a locking ring configuredto be arranged around the head receiving portion. The locking ringincludes an engagement structure for engagement with a tool to allow thelocking ring to be moved out of the locking position, i.e. releasing thelocking mechanism. This enables a surgeon or other practitioner to carryout revisions or further positioning or re-positioning of the angularposition of a receiving part with respect to the bone anchoring element.

SUMMARY

In spinal surgery, often multiple segments of the spinal column have tobe corrected and/or stabilized using a spinal rod and polyaxial boneanchors. During such a procedure, repeated adjustments of the boneanchoring elements and the rod relative to the receiving parts ofrespective polyaxial bone anchoring devices may become necessary.

It is an object of the invention to provide a polyaxial bone anchoringdevice having an outer locking ring that allows for improved handlingduring surgery, and to provide an instrument adapted for use with such apolyaxial bone anchoring device.

With such a polyaxial bone anchoring device and instrument, a user canmove the locking ring relative to the receiving part from a non lockingposition where the head is pivotable relative to the receiving part to alocking position where the head is locked, and vice-versa, by displacingan outer tube of the instrument relative to an inner tube of theinstrument. The instrument can be used when the rod and a lockingelement are already inserted into a rod receiving portion of thereceiving part, but when the rod is not yet fixed. A temporary lockingof the bone anchoring element in the receiving part can be effectedusing the instrument. Therefore, the locking element is not needed forthe temporary locking of the head. As a result, the polyaxial boneanchoring device allows a user to adjust or re-adjust an angularposition of the receiving part relative to the bone anchoring elementseveral times while the rod is already inserted.

Moreover, the head of the bone anchoring element can be locked andreleased relative to the receiving part independently of locking of therod. Similarly, the rod can also be locked and released independently oflocking of the head of bone anchoring element. Therefore, the functionof the polyaxial bone anchoring device in combination with theinstrument is similar to that of a polyaxial bone anchoring device withan inner compression member and a two-part locking element, wherein thehead and the rod can be locked independently.

In a locking position of the locking ring that has been achieved withthe aid of the instrument, it is further possible to pull the boneanchoring device with the instrument towards the inserted rod, therebyalso pulling the associated vertebra towards the rod, for correcting aposition of the corresponding vertebra.

The locking ring can also assume an insertion position for inserting thehead of the bone anchoring element into a head receiving portion of thereceiving part. The instrument can be used for placing the receivingpart with the locking ring in the insertion position onto a head of abone anchoring element that has already been inserted in bone.

A system including the polyaxial bone anchoring device and theinstrument adapted thereto is also provided. Furthermore, the instrumentalso permits a drive tool to be guided therethrough for tightening thelocking element for fixing the rod.

With such a polyaxial bone anchoring device and instrument, variousadjustments and re-adjustments of angular positions and/or rod positionscan be more easily performed during surgery, without applying largerforces that could result in damage to surrounding material, such astissue, blood vessels, or nerves. Revisions or secondary adjustments ofthe rod and the receiving part relative to the bone anchoring elementcan thus be performed in a more controlled manner.

In addition, with a polyaxial bone anchoring device according toembodiments of the invention, a modular system can be provided thatallows for combining of various bone anchoring elements with thereceiving part, on demand, depending on the actual clinical requirementsin each specific case. This reduces the overall cost of using polyaxialscrews, reduces inventory, and gives a surgeon a wider or more versatilechoice of implants.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the invention will become apparentfrom the description of embodiments by means of the accompanyingdrawings. In the drawings:

FIG. 1 shows an exploded perspective view of a first embodiment of apolyaxial bone anchoring device;

FIG. 2 shows a perspective view of the polyaxial bone anchoring deviceof FIG. 1 in an assembled state;

FIG. 3 shows a perspective view of the polyaxial bone anchoring deviceof FIG. 2 rotated by about 90°;

FIG. 4 shows an enlarged cross-sectional view of the polyaxial boneanchoring device of FIGS. 1 to 3, the cross-section taken in a planeperpendicular to an axis of an inserted rod and extending through thecenter of a receiving part of the bone anchoring device;

FIG. 5 shows a perspective view of a front portion of an instrumentadapted for use with the polyaxial bone anchoring device in FIGS. 1 to4;

FIGS. 6a to 6c show perspective views of steps of connecting theinstrument of FIG. 5 with the polyaxial bone anchoring device of FIGS. 1to 4;

FIGS. 7a to 7c show cross-sectional views of steps of actuating thelocking ring relative to the receiving part using the instrument, thecross-sections taken in a plane extending through the center of thereceiving part and arranged at an angle of about 45° relative to theaxis of the inserted rod;

FIG. 8 shows a cross-sectional view of a step of locking a rod in a rodrecess of the receiving part using a tool extending through theinstrument, the cross-section taken in a plane extending through thecenter of the receiving part and arranged at an angle of about 45°relative to the axis of the inserted rod;

FIG. 9 shows a perspective view of a front portion of a secondembodiment of an instrument;

FIG. 10 shows a cross-sectional view of a second embodiment of thepolyaxial bone anchoring device with the instrument shown in FIG. 9attached, the cross-section taken in a plane extending through thecenter of the receiving part and arranged at an angle of about 45°relative to the axis of the inserted rod; and

FIG. 11 shows a front portion of a third embodiment of an instrument.

DETAILED DESCRIPTION

As shown in FIGS. 1 to 4, a bone anchoring device according to anembodiment of the invention includes a bone anchoring element 1 in theform of, for example, a bone screw having a shank 2 with a threadedportion and a head 3 with a spherically-shaped outer surface portion.The head 3 has a recess 4 for engagement with a driver or tool. The boneanchoring device also includes a receiving part 5 for receiving a rod 6to be connected to the bone anchoring element 1. Further, a fixationelement 7 in the form of, for example, an inner screw or set screw maybe provided for fixing the rod 6 in the receiving part 5. In addition,the bone anchoring device includes a locking ring 8 for locking the head3 in the receiving part 5.

The receiving part 5 has a rod receiving portion 9, which may have anouter shape that is substantially cylindrical. The rod receiving portion9 has a first end 9 a and an opposite second end 9 b, and a central axisC that passes through the first end 9 a and the second end 9 b. Thefirst end 9 a may serve as an abutment for a portion of the instrument,as described in greater detail below. A coaxial first bore 10 isprovided at the second end 9 b, as shown, for example in FIG. 4. Adiameter of the first bore 10 is smaller than a diameter of the head 3of the bone anchoring element 1. The rod receiving portion 9 furtherincludes a coaxial second bore 11 extending from the first end 9 a to adistance from the second end 9 b. A diameter of the second bore 11 islarger than the diameter of the first bore 10. At a distance from thefirst end 9 a, a circumferential groove 9 c is provided that has a lowerwall 9 c′ which extends at an acute angle with respect to the centralaxis C, or in other words, with respect to a bottom of the groove 9 c.At approximately the same axial position, an internal groove 9 d isprovided that may have a portion with a V-shaped cross-section. At theaxial position corresponding to the lower wall 9 c′ of the groove 9 cand to the internal groove 9 d, the wall thickness of the rod receivingportion 9 is reduced to provide a break-off area.

A substantially U-shaped recess 12 extends from the first end 9 a in thedirection of the second end 9 b in the rod receiving portion 9, whereina width of the recess 12 is slightly larger than a diameter of the rod6, such that the rod 6 can be placed in the recess 12 and can be guidedtherein. By means of the recess 12, two free legs 12 a, 12 b are formed,on which an internal thread 13 may be provided. The internal thread 13can be, for example, a metric thread, a flat thread, a negativeangle-thread, a saw-tooth thread, or any other thread form. Preferably,a thread form such as a flat thread or a negative angle thread is usedto prevent or reduce splaying of the legs 12 a, 12 b when the innerscrew 7 is screwed-in. A portion of the legs 12 a, 12 b above the outergroove 9 c form extended tabs that can be broken off The depth of therecess 12 is such that when the rod 6 is placed into the recess 12 andthe locking element 7 is screwed between the legs 12 a, 12 b, thelocking element 7 does not substantially protrude out of the receivingpart 5 when the extended tabs have been broken off.

At an outer surface of the rod receiving portion 9 an engagementstructure for engagement with the instrument is provided, wherein theengagement structure may be formed by a plurality of circumferentialribs 14 a, 14 b. In the embodiment shown, on each leg 12 a, 12 b tworibs 14 a, 14 b, are respectively provided. The ribs 14 a, 14 b arepositioned between the groove 9 c and the second end 9 b of the rodreceiving portion 9. Each of the plurality of ribs 14 a, 14 b extendsover a segment of the circumference of the rod receiving portion 9, forexample, for approximately a quarter circle. The arrangement is suchthat one end of each rib 14 a, 14 b is positioned at the rod receivingrecess 12 and the other end of each rib ends approximately to the middleof each leg 12 a, 12 b. Hence, in a circumferential direction, there isa rib-free surface portion 15 a, 15 b on the outer surface of each leg12 a, 12 b, where the ribs 14 a, 14 b are not present. Furthermore, theribs 14 a, 14 b are arranged in an asymmetric manner with respect to aplane extending through the central axis C and a longitudinal axis L ofthe rod receiving recess 12. More specifically, the position of the ribs14 a, 14 b is offset by 180° measured in relation to the central axis C,and is rotated with respect to the central axis C such that the ribs 14a of the leg 12 a extend to the rod receiving recess 12 at one side ofthe receiving part 5 and the ribs 14 b extend to the rod receivingrecess 12 at the other side of the receiving part 5. This permits theinstrument to be placed first onto the rib-free portions 15 a, 15 b, andthen to be rotated to engage the ribs 14 a, 14 b, as described ingreater detail below. The ribs 14 a, 14 b may have a substantiallyrectangular cross-section and may have inclined end portions. It shallbe understood that the number of ribs on each leg 12 a, 12 b is notlimited to two, but one single rib or more than two ribs may be providedon each leg in other embodiments. Also the shape of the ribs may bedifferent in other embodiments.

As can be seen in particular in FIG. 1, cut-outs 16 are provided in therod receiving portion 9, which extend from the second end 9 b to therecess 12. The cut-outs 16 are provided on either end of the channelformed by the recess 12.

Meanwhile, the locking element 7, in the form of an inner screw, has athread corresponding to the internal thread 13 provides on the legs 12a, 12 b.

On an outer surface of the rod receiving portion 9, in the region of thelegs 12 a, 12 b, a groove 17 may be provided that extends in acircumferential direction and serves for engagement with a portion ofthe locking ring 8. The groove 17 may be asymmetric to allow fordisengagement of the locking ring 8 from the groove 17 when the lockingring 8 is shifted downwards, away from the first end 9 a.

At the side of the second end 9 b, the receiving part 5 further includesa head receiving portion 18 providing an accommodation space for thehead 3 of the bone anchoring element 1. The head receiving portion 18has a greatest outer diameter that is smaller than a greatest outerdiameter of the rod receiving portion 9. An internal hollow section 19forms a seat for the head 3 of the bone anchoring element 1, and is openvia an opening 20 to a free end 18 b of the head receiving portion 18.The internal hollow section 19 has a shape adapted to the shape of thehead 3. In the embodiment shown, the internal hollow section 19 is aspherical section to accommodate the spherical head 3. Moreover, thehollow section 19 is configured to encompass the head 3 of the boneanchoring element 1 from the side, to cover a region including a largestdiameter of the head 3. A plurality of slits 21 are provided in the headreceiving portion 18 that are open to the free end 18 b. The slits 21render the head receiving portion 18 flexible so that the head receivingportion 18 can be compressed to clamp and lock an inserted head 3 in thehollow internal portion 19 by means of friction. A number and size ofthe slits 21 is provided depending on the desired flexibility of thehead receiving portion 18. The flexibility of the head receiving portion18 is such that the head 3 of the bone anchoring element 1 can beinserted into the hollow internal portion 19 by expanding the headreceiving portion 18, and can be clamped by compressing the headreceiving portion 18.

As illustrated in particular in FIGS. 1 and 4, an outer surface of thehead receiving portion 18 has a first section 22 with an outer diameterthat increases towards the free end 18 b, for example, in an outwardlycurved or conically widening manner. Adjacent to the first section 22,there may be a circumferential groove 23 that is recessed with respectto the first section 22 and that serves for engagement with a portion ofthe locking ring 8. The groove 23 may be shaped so as to allow fordisengagement of the locking ring 8 from the groove 23 (i.e., for movinga portion of the locking ring 8 out of the groove 23) when the lockingring 8 is moved in a direction towards the free end 18 b (or away fromthe first end 9 a of the rod receiving portion 9). This is realized, forexample, by having a lower wall of the groove 23 that is inclined andwidens towards the free end 18 b. Adjacent to the groove 23, there is athird portion 24 of the head receiving portion 18 with a substantiallycylindrical outer surface. The third portion 24 may be configured tocooperate with a portion of the locking ring 8 to enhance a clampingeffect of the locking ring 8 on the head receiving portion 18.

The locking ring may 8 include a portion that is substantiallycylindrical, and has an upper end and a lower end. In a mounted state,the upper end faces towards the first end 9 a of the rod receivingportion 9, and the lower end is oriented in the direction of the freeend 18 b of the head receiving portion 18. Approximately in a centralregion of the locking ring 8, at an inner wall, a first portion 81 isprovided that cooperates with the first outer surface portion 22 of thehead receiving portion 18 to compress the head receiving portion 18. Thefirst portion 81 may be tapered, straight, or curved, for example, witha curvature directed towards a center of the locking ring 8. At thelower end, there is an inwardly projecting edge 82, an inner diameter ofwhich may be smaller than an inner diameter of other portions of thelocking ring 8. The inwardly projecting edge 82 is configured to engagethe groove 23 of the head receiving portion 18, and to engage thecylindrical portion 24 of the head receiving portion 18 when the boneanchoring device is in a locked state.

The locking ring also includes upwardly extending wall portions 83 athat are separated from each other by slits 84. The upwardly extendingwall portions 83 a are arranged at an outer circumference or region ofan inner circumferential shoulder 85 of the locking ring 8, and renderthe upper portion of the locking ring 8 flexible. A number and size ofthe slits 84 and a thickness of the wall portions 83 a are configuredsuch that a desired flexibility is obtained. At respective free ends ofthe wall portions 83 a, the wall portions 83 a are configured to engagethe groove 17 provided on the outer surface of the rod receiving portion9.

Two projections 86 that are located diametrically opposite to each otherare also formed at the locking ring 8. The projections 86 have a heightsuch that they extend through the cut-outs 16 of the receiving part 5and project above a bottom of the substantially U-shaped recess 12 whenthe locking ring 8 is in a position where the shoulder 85 abuts thesecond end 9 b of the rod receiving portion 9. A free end surface of theprojection 86 forms a rod support surface. The locking ring 8 isarranged around the head receiving portion 18 of the receiving part 5such that the projections 86 are located at the positions of the recess12. By means of this, the projections 86 and the cut-outs 16 prevent thelocking ring 8 from rotating relative to the receiving part 5 when therod 6 is not yet inserted in the recess 12.

The locking ring 8 further includes on its outer surface an engagementstructure for engagement with the instrument described in more detailbelow. The engagement structure includes a plurality of ribs 88 a, 88 bthat are arranged on an outer surface of the locking ring 8 between theflexible wall portions 83 a and the lower end of the locking ring 8. Theribs 88 a, 88 b extend over a segment of an outer circumference of thelocking ring 8, for example, for approximately a quarter circle or lessthan a quarter circle. In the embodiment shown, the ribs include twopairs 88 a, 88 b of ribs that are arranged diametrically opposite to oneanother. Each pair 88 a, 88 b includes two axially spaced apart ribsextending in a circumferential direction on each side of the lockingring 8. The position of the ribs in a circumferential directioncorresponds to the position of the ribs 14 a, 14 b of the rod receivingportion 9 when the locking ring 8 is mounted around the head receivingportion 18 and the projections 86 extend into the cut-outs 16. In otherwords, one group of ribs 88 a extends circumferentially around thelocking ring 8 from a circumferential position adjacent to oneprojection 86 to a certain distance therefrom, and the opposite group ofribs 88 b extends circumferentially from a position adjacent to theopposite projection 86 to a certain distance therefrom. By means ofthis, rib-free surfaces 25 a, 25 b are formed between the ribs 88 a, 88b, that are aligned with the rib-free surfaces 15 a, 15 b when thelocking ring 8 is mounted around the receiving part 5. The ribs 88 a, 88b may have substantially rectangular cross-sections and inclined endportions in a circumferential direction. It shall be noted, however,that the shape of the ribs may be different in other embodiments. Also,in other embodiments, there may be one single rib or more than two ribson each side of the locking ring.

Because the head receiving portion 18 is flexible, the locking ring 8can be mounted onto the receiving part 5 from the free end 18 b of thehead receiving portion 18.

In an embodiment of the invention, the locking ring 8 can assume threemain positions relative to the receiving part 5. In a first position(not shown), the inwardly projecting edge 82 of the locking ring 8engages or is positioned adjacent to the groove 23 of the head receivingportion 18. In this position, the head 3 of the bone anchoring element 1can be inserted into the internal hollows space 19 of the receiving part5 from the free end 18 b of the head receiving portion 18. The lockingring 8 is prevented from moving further upwards towards the first end 9a of the rod receiving portion 9 because the shoulder 85 abuts againstthe second end 9 b of the rod receiving portion 9 in this position. Thisposition may also be referred to as an insertion position.

In a second position, the locking ring 8 is shifted towards the free end18 b of the head receiving portion 18 until the flexible wall sections83 a snap with their free ends into the groove 17 of the rod receivingportion 9. In this position, the head 3 is not yet locked, but may beprevented from removal out of the internal hollow space 19. In someembodiments, the head 3 may also be frictionally clamped in this stateto such an extent that the bone anchoring element 1 is still pivotablerelative to the receiving part 5 when a force, for example, a manuallyapplied force, is applied to the bone anchoring device to overcome thefriction force. This position may also be referred to as a pre-lockingposition.

In a third position, the locking ring 8 is shifted further towards thefree end 18 b of the head receiving portion 18 (or away from the firstend 9 a of the rod receiving portion 9), such that the head 3 is finallylocked relative to the receiving part 5. In this position, the headreceiving portion 18 is compressed by the locking ring 8, so that thehead 3 cannot move and is fixed at an angular position with respect tothe receiving part 5. In this position, there is a gap formed betweenupper ends of the flexible wall sections 83 a and the groove 17.

The receiving part 5, the locking ring 8, the locking element 7, and thebone anchoring element 1 may each be made of bio-compatible materials,for example of titanium or stainless steel, of a bio-compatible alloy,such as a NiTi-alloys, for example Nitinol, magnesium or magnesiumalloys, or from a bio-compatible plastic material, such as, for example,polyether ether ketone (PEEK) or poly-1-lactide acid (PLLA). Inaddition, the parts can be made of the same as or of different materialsfrom one another.

Turning now to FIG. 5, an instrument that is adapted for use with thepolyaxial bone anchoring device according to FIGS. 1 to 4 will bedescribed. The instrument 50 includes an outer tube 51 and an inner tube61, wherein the outer tube 51 and the inner tube 61 are axiallydisplaceable relative to each other along a longitudinal axis of thetubes. Preferably, the outer tube 51 and the inner tube 61 are securedagainst rotation relative to each other, so that rotating the outer tube51 also rotates the inner tube 61, and vice-versa. Preferably the axialposition of the inner tube 61 relative to the outer tube 51 can belocked. The displacement of the inner tube and the outer tube relativeto each other can be effected, for example, by a lever (not shown), suchas a toggle lever, whereby a first end of a first lever arm is connectedto the outer tube 51 and a first end of a second lever arm is connectedto the inner tube 61, and where second ends of the lever arms can beactuated by hand. This is, however, only an example, and any othermechanism for displacing and locking the tubes 51, 61 relative to eachother can also be implemented.

The outer tube 51 and the inner tube 61 each has a front portion 52, 62.An outer surface of the front portion 52 of the outer tube may beslightly tapered towards a free end 51 a of the outer tube 51. At leastthe front portion 62 of the inner tube 61 may be guided in the frontportion 52 of the outer tube 51. A free end 61 a of the inner tube 61may abut against a circumferentially extending shoulder 52 a on an innerwall of the outer tube 51. Further, a recess 53 is formed that extendsfrom the free end 51 a of the outer tube 51, and through the frontportion 52 of the outer tube 51 and the front portion 62 of the innertube 61. The recess 53 has an inner diameter or width that is at leastas large as an outer diameter of the receiving part 5 in the region ofthe rib-free surfaces 15 a, 15 b and as an outer diameter of the lockingring 8 in the region of the rib-free surfaces 25 a, 25 b, such that theinstrument 50 can be placed onto and around the receiving part 5 and thelocking ring 8. A length of the recess 53 in an axial direction is suchthat the receiving part 5 can be accommodated in the front portion 52,62 of the tubes 51, 61 instrument 50. Thus, the inserted rod 6 can alsoextend through the recess 53. At a distance from the free end 61 a ofthe inner tube 61, an inner shoulder 63, for example an annularshoulder, is formed, which serves as an abutment for the first end 9 aof the rod receiving portion 9 of the receiving part 5. By means of therecess 53, two free legs 54 a, 54 b are formed on the instrument 50. Theshape of the recess 53 is such that the width of the legs 54 a, 54 b maydecrease towards the free end 51 a. This facilitates easier finding ofthe receiving part 5 in-situ, and placing of the instrument 50 onto thereceiving part 5 and the locking ring 8 in-situ during surgery.

At a distance from the free end 51 a, the outer tube 51 definescircumferentially extending grooves 55 a, 55 b in an inner wall of thelegs 54 a, 54 b, respectively. The number and shape of the grooves 55 a,55 b corresponds to the number and shape of the ribs 88 a, 88 b of thelocking ring 8. In the embodiment shown, two axially spaced apartgrooves 55 a, 55 b are provided on each side. The grooves 55 a, 55 b areconfigured to engage the ribs 88 a, 88 b of the locking ring 8.Similarly, circumferentially extending grooves 65 a, 65 b are providedat an inner wall of the inner tube 61 at a distance from the free end 61a. The grooves 65 a, 65 b are configured to cooperate with the ribs 14a, 14 b of the rod receiving portion 9. When the inner tube 61 is at anengagement position of the instrument 50, described in greater detailbelow, the distance between the grooves 55 a, 55 b of the outer tube 51and the grooves 65 a, 65 b of the inner tube 61 corresponds to thedistance between the ribs 88 a, 88 b on the locking ring 8 and the ribs14 a, 14 b on the rod receiving portion 9 when the locking ring 8 is inthe pre-locking position.

The instrument 50 as a whole, or parts thereof, may be made of one ormore of the same materials mentioned above with respect to the polyaxialbone anchoring device.

The operation of the instrument 50 will now be described with referenceto FIGS. 6a to 7c . First, FIGS. 6a to FIGS. 6c show steps of placingthe instrument 50 onto the receiving part 5. In FIG. 6a , the boneanchoring element 1 may already be inserted into a bone. The lockingring 8 is in the pre-locking position, where the flexible wall portions83 a abut against an upper wall of the groove 17 of the rod receivingportion 9. The rod 6 and the locking element 7 may already be insertedin the receiving part 5, but the locking element 7 is not tightened sothat the rod 6 is still movable along the rod axis and also has somespace for moving axially up and down. The front portion of theinstrument 50 is oriented such that the legs 54 a, 54 b are aligned withthe rib-free surface portions 15 a, 15 b of the rod receiving portion 9and the rib-free surface portions 25 a, 25 b of the locking ring 8.Then, as depicted in FIG. 6b , the instrument 50 is moved downwardrelative to the receiving part 5 so that the legs 54 a, 54 b are placedover the receiving part 5 until the first end 9 a of the receiving partabuts against the inner shoulder 63 of the inner tube 61. In thisposition, the inner grooves 55 a, 55 b of the locking ring are at a sameaxial position as the ribs 88 a, 88 b of the locking ring 8, and theinner grooves 65 a, 65 b of the inner tube 61 are at a same axialposition as the ribs 14 a, 14 b of the rod receiving portion 9.Therefore, when the instrument 50 is rotated, the grooves 55 a, 55 b ofthe outer tube 51 engage the ribs 88 a, 88 b of the locking ring 8, andat the same time, the grooves 65 a, 65 b of the inner tube 61 engage theribs 14 a, 14 b of the rod receiving portion 9, as shown in FIG. 6 c.

The cooperation of the engagement structures in the form of ribs andgrooves connects the outer tube 51 to the locking ring 8 and the innertube 61 to the receiving part 5 in form-fit manners, respectively, suchthat a force for moving the locking ring 8 relative to the receivingpart 5 in an axial direction can be transmitted through the instrument50.

FIGS. 7a to 7c illustrate the use of the instrument 50 for both lockingof the head 3 and releasing the lock on the head 3 relative to thereceiving part 5. In FIG. 7a , the locking ring 8 is in the pre-lockingposition, which means that the flexible wall portions 83 a abut againstthe upper wall of the outer grooves 17 on the rod receiving portion 9.The head 3 is pivotable in the head receiving portion 18, but cannot bepulled out through the lower opening 20. The receiving part 5 is held bythe inner tube 61 in a form-fit manner, so that the receiving part 5cannot move relative to the inner tube 61, at least in an axialdirection. The locking ring 8 is engaged by the outer tube 51.

As can be seen further in the figures, an inner diameter of the innertube 61 above the shoulder 63 is such that the locking element 7 can beinserted through the inner tube 61 and into the rod receiving portion 9of the receiving part 5.

In the next step, as depicted in FIG. 7b , the outer tube 51 is moveddownward relative to the inner tube 61, so that the inner edge 82 of thelocking ring 8 presses more against the lower portion 24 of the headreceiving portion 18 and the first portion 81 of the locking ring 8further compresses the first outer surface portion 22 of the headreceiving portion 18, to lock the head 3 therein. Meanwhile, the rod isstill movable to allow adjustments of the rod position relative to thereceiving part 5. In this locking position of the locking ring 8, asshown in FIG. 7b , the instrument 50 can also be used to pull the boneanchoring device towards the inserted rod 6, to correct a position ofthe associated vertebra.

Next, for performing further adjustments, the lock on the head can bereleased, as depicted in FIG. 7c . The outer tube 51 can be pulled upuntil the shoulder 52 a abuts against the free end 61 a of the innertube 61. Thereby, the locking ring 8 is moved upward out of the lockingposition and back into the pre-locking position, which is the sameposition depicted in FIG. 7 a.

With the possibility of locking the head 3 and then also releasing thelocked head 3 while the rod 6 and the locking element 7 are alreadyinserted in the receiving part 5, a greater variety of adjustment stepscan be carried out, which simplifies the surgical procedure.

Finally, once a correct angular position of the head 3 and a correctposition of the receiving part 5 relative to the rod 6 has been found,the locking element 7 can be tightened, for example, with a drive tool70 that is inserted through the inner tube 61 and that engages thelocking element 7. Tightening the locking element 7 moves the rod 6downwards, which in turn presses the rod 6 onto the rod support surfaces86 of the locking ring 8 to also move the locking ring 8 down relativeto the receiving part 5. Thereby the head 3 and the rod 6 are lockedsimultaneously by the locking element 7. The instrument 50 can then beremoved by rotating the instrument 50 so that the grooves 55 a, 55 b,disengage from the ribs 88 a, 88 b, and so that the legs 54 a, 54 b arealigned with the rib-free surfaces 15 a, 15 b, 25 a, 25 b. In thisposition, the instrument 50 can be pulled away from the receiving part5. The extended tabs at the first end 9 a of the rod receiving portion 9of the receiving part 5 may be broken off at the end of the procedure.

In a surgical operation, a plurality of bone anchoring devices areconnected by the rod. It may be possible to use several instruments 50for several bone anchoring devices simultaneously, which facilitates thesteps such as the adjustment, re-positioning, etc., of each boneanchoring device relative to the rod.

A further embodiment of a bone-anchoring device and instrument is shownin FIGS. 9 and 10. The embodiment of the bone anchoring device and theinstrument in FIGS. 9 and 10 differs from the previous embodiments onlyin the engagement structures for the instrument and the bone anchoringdevice. All other parts are the same or similar to the previouslydescribed embodiments, and are indicated with the same referencenumerals as in the previous embodiments, and their descriptionstherefore will not be repeated. The receiving part 5′ has in the rodreceiving portion 9 a single groove 140 a, 140 b at an outer wall ofeach of the legs 12 a, 12 b. The circumferential extending groove 140 a,140 b is located at a distance from the outer groove 9 c. The instrument50′ has a corresponding circumferential projection 650 a, 650 b at aninner wall of the inner tube 61. The inner projection 650 a, 650 b is ata position and is shaped so as to be able to engage the groove 140 a,140 b at the receiving part 5′.

Similarly, a single groove 880 a, 880 b is provided at an outer surfaceof the locking ring 8′. A corresponding circumferential rib 550 a, 550 bis provided at an inner surface of the outer tube 51. The rib 550 a, 550b is configured to engage the groove 880 a, 880 b at the locking ring8′. Hence, in contrast to the first embodiment, grooves are provided atthe receiving part 5′ and projections or ribs are provided at theinstrument 50′. The function and operation of the parts may be the sameas or similar to that of the first embodiment.

A further modified tool embodiment which facilitates easier outwardsplaying of the legs 54 a, 54 b is depicted in FIG. 11. Like numeralsdenote the same or similar parts as in the previous embodiments. In theinstrument 50″ shown in FIG. 11, the outer tube 51 and the inner tube 61are both provided with slots 69 a, 69 b, which allow legs 54 a, 54 b tospread apart more easily when the instrument 50″ is moved downwardrelative to the bone anchoring device, similarly as shown in FIGS. 6aand 6b . The circumferential ribs or projections 550 a, 550 b, 650 a,650 b may thus slide over outer surfaces of the receiving part andlocking ring, respectively, and snap into or otherwise engagecorresponding grooves 140 a, 140 b, 880 a, 880 b. Depending on theparticular design of the tool and/or the bone anchoring device, afurther rotation step for engaging the respective parts may or may notbe necessary.

Further modifications can also be contemplated. For example, on each ofthe receiving part and/or on the locking ring, a combination of ribs andgrooves can be provided, and the instrument may have a counterpart orcomplementary structure, or in other words, a combination of grooves andribs configured to engage the structures at the receiving part. Theshape and the number of the engagement elements may also vary. The ribsand grooves need not extend circumferentially in a plane in someembodiments, but can instead extend along a helix-shape, for example.Therefore, the engagement structures on the instrument, the receivingpart, and the locking ring can also be realized with, for example,threads. Other engagement structures may also be contemplated thatprovide a form-fit connection which can transmit forces onto the boneanchoring device and which can be effected by a rotating and/or slidingmovement of the instrument relative to the bone anchoring device. Insome embodiments, the engagement structures may also be provided on onlyone side of the rod receiving portion and one side of the locking ring.

The bone anchoring device according to other embodiments of theinvention can be provided in further modified forms. For example, thehead of the bone anchoring element can have any other shape, such as,for example, a cylindrical shape, whereby a monoaxial bone screw isprovided, allowing rotation of a screw element around a single axis withrespect to the receiving part. The head can also be conically shaped orotherwise shaped, with the internal hollow section of the head receivingportion adapted to the specific shape. In a further modification, theflexibility of the head receiving portion may be based on or facilitatedby properties of the material, for example, a plastic material may beused, and the slits in the head receiving portion may be fully or partlyomitted.

The projections at the locking ring that form a support surface for therod can also have various other shapes, such as circular, v-shaped, or aflat shape. The projections can also be omitted in some embodiments.

In some embodiments, the head receiving portion can have an inclinedopen end or can be otherwise asymmetric to allow for a greaterangulation of an inserted head in one direction.

The outer surface of the head receiving portion and the inner surface ofthe locking ring can also have various other shapes that result incompression of the head receiving portion by the locking ring by meansof an increasing force when the locking ring is shifted downward. Alsothe locking ring can have various other designs. For example, thelocking ring can be formed without the flexible wall sections.

The extended tabs on the receiving part can be omitted. In addition, insome embodiments, other kinds of locking elements can also be used, forexample, non threaded locking elements that have an alternativeadvancement structure. In addition, all kinds of bone anchoring elementscan be used, such as, for example, nails or bone anchors with barbs.

Meanwhile, the use of the instrument has been shown in connection withan already assembled bone anchoring device, it is also contemplated thatthe instruments can be used for the in-situ placement of a receivingpart with a mounted locking ring onto a bone anchoring element that hasalready been inserted into a bone. In this case, the locking ring wouldbe at an insertion position, and the instrument would be configured toengage the bone anchoring device while the locking ring is at theinsertion position. This can be realized, for example, by using anengagement structure in the form of a thread and a design where the tubeportions are also rotatable relative to each other.

While the present invention has been described in connection withcertain exemplary embodiments, it is to be understood that the inventionis not limited to the disclosed embodiments, but is instead intended tocover various modifications and equivalent arrangements included withinthe spirit and scope of the appended claims, and equivalents thereof.

1. A bone anchoring device comprising: a receiving part for coupling arod to a bone anchoring element, the receiving part comprising: a rodreceiving portion having a first end, a second end, a central axisextending between the first end and the second end, and a recess forreceiving the rod, the recess extending from the first end towards thesecond end and forming two free legs, the rod receiving portion furtherhaving an outer surface and a first engagement structure on the outersurface of the rod receiving portion that extends farther radiallyoutwardly than all of the other parts of the rod receiving portion; anda head receiving portion at the second end of the rod receiving portionfor accommodating a head of the bone anchoring element, the headreceiving portion having a free end and being flexible for inserting andclamping the head; and a locking ring configured to be arranged aroundthe head receiving portion, the locking ring having an outer surface anda second engagement structure on the outer surface of the locking ringthat extends farther radially outwardly than the outer surface of therod receiving portion; wherein when the locking ring is around the headreceiving portion, the locking ring can assume a locking position wherethe locking ring exerts a force on the head receiving portion to lock aninserted head; and wherein the first engagement structure and the secondengagement structure are configured to be engaged by an instrument tomove the locking ring relative to the receiving part along the centralaxis from the locking position towards the first end of the rodreceiving portion to a position where the inserted head is pivotable. 2.(canceled)
 3. The bone anchoring device of claim 1, wherein the firstengagement structure is arranged at a distance from the first end of therod receiving portion.
 4. The bone anchoring device of claim 1, whereinthe second engagement structure is arranged at a distance from a firstend of the locking ring that faces away from the first end of the rodreceiving portion.
 5. The bone anchoring device of claim 1, wherein thelocking ring further comprises a rod support surface which is alignedwith the recess of the rod receiving portion when the locking ring isaround the head receiving portion, and wherein the first engagementstructure and the second engagement structure are arranged asymmetricwith respect to a plane extending through the central axis of thereceiving part and a longitudinal axis of the recess.
 6. (canceled) 7.The bone anchoring device of claim 1, wherein the first engagementstructure comprises at least one circumferentially extending rib or atleast one circumferentially extending groove at each of the legs thatextends over a segment of the outer surface of the leg.
 8. The boneanchoring device of claim 1, wherein the second engagement structurecomprises at least two circumferentially extending ribs or at least twocircumferentially extending grooves that extend over a segment of theouter surface of the locking ring.
 9. A system comprising the boneanchoring device of claim 1 and an instrument for use with the boneanchoring device, the instrument comprising: an outer tube having athird engagement structure for engaging the second engagement structureat the locking ring; and an inner tube extending at least partially inthe outer tube, the inner tube having a fourth engagement structure forengaging the first engagement structure at the rod receiving portion;wherein the inner tube is movable axially relative to the outer tube formoving the locking ring axially relative to the receiving part. 10-12.(canceled)
 13. The system of claim 9, wherein the third and fourthengagement structures have shapes that are complimentary to the shapesof the second and first engagement structures, respectively. 14.(canceled)
 15. The system of claim 9, wherein the instrument isconfigured to engage the polyaxial bone anchoring device such that thelocking ring and the receiving part are movable relative to each otherby displacing the outer tube relative to the inner tube.
 16. The systemof claim 9, wherein the instrument is configured to engage the boneanchoring device upon rotation of the instrument relative to the centralaxis of the bone anchoring device.
 17. The bone anchoring device ofclaim 1, wherein the first engagement structure extendscircumferentially around the outer surface of each of the legs and has alength that is shorter than a circumferential width of the outer surfaceof each of the legs.
 18. The bone anchoring device of claim 1, whereinthe second engagement structure extends circumferentially around theouter surface of the locking ring and has a length that is shorter thana circumferential width of the outer surface of each of the legs.
 19. Aninstrument for adjusting a bone anchoring device comprising a receivingpart with a rod receiving portion having a first end, a second end, acentral axis extending between the first end and the second end, and arecess for receiving a rod, the recess extending from the first endtowards the second end and forming two free legs, the rod receivingportion further having a first engagement structure, and a headreceiving portion at the second end of the rod receiving portion foraccommodating a head of the bone anchoring element, the head receivingportion having a free end and being flexible for inserting and clampingthe head, and a locking ring configured to be arranged around the headreceiving portion, the locking ring having a second engagementstructure, wherein when the locking ring is around the head receivingportion, the locking ring can assume a locking position where thelocking ring exerts a force on the head receiving portion to lock aninserted head, the instrument comprising: an outer tube having a thirdengagement structure for engaging the second engagement structure at thelocking ring; and an inner tube extending at least partially in theouter tube, the inner tube having a fourth engagement structure forengaging the first engagement structure at the rod receiving portion;wherein the inner tube is movable axially relative to the outer tube formoving the locking ring axially relative to the receiving part from thelocking position towards the first end of the rod receiving portion to aposition where the inserted head is pivotable.
 20. The instrument ofclaim 19, wherein the inner tube and the outer tube each comprises arecess extending from a first end towards a second end for passing a rodtherethrough.
 21. The instrument of claim 20, wherein the recess has asubstantially inverted U-shape, thereby forming two free legs at thefirst end of each of the inner tube and the outer tube.
 22. Theinstrument of claim 21, wherein a width of each of the legs in acircumferential direction decreases towards the first end.
 23. Theinstrument of claim 19, wherein the inner tube is rotationally fixedrelative to the outer tube.
 24. A method of attaching a bone anchoringdevice to a bone, the bone anchoring device comprising a bone anchoringelement with a head and a shank, a receiving part for coupling a rod tothe bone anchoring element, the receiving part comprising a rodreceiving portion having a first end, a second end, a central axisextending between the first end and the second end, and a recess forreceiving the rod, the recess extending from the first end towards thesecond end and forming two free legs, the rod receiving portion furtherhaving an outer surface and a first engagement structure on the outersurface of the rod receiving portion that extends farther radiallyoutwardly than all of the other parts of the rod receiving portion, anda head receiving portion at the second end of the rod receiving portionfor accommodating a head of the bone anchoring element, the headreceiving portion having a free end and being flexible for inserting andclamping the head, and a locking ring configured to be arranged aroundthe head receiving portion, the locking ring having an outer surface anda second engagement structure on the outer surface of the locking ringthat extends farther radially outwardly than the outer surface of therod receiving portion, the method comprising: inserting the shank of thebone anchoring element in a bone; adjusting an angular position of thereceiving part relative to the bone anchoring element; and moving thelocking ring to a locking position when the head is in the headreceiving portion and the locking ring is around the head receivingportion, where the locking ring exerts a force on the head receivingportion to lock an inserted head, and wherein the first engagementstructure and the second engagement structure are configured to beengaged by an instrument to move the locking ring relative to thereceiving part along the central axis from the locking position towardsthe first end of the rod receiving portion to a position where theinserted head is pivotable.
 25. The method of claim 24, furthercomprising: engaging the first and second engagement structures with aninstrument; adjusting the instrument to move the locking ring axiallyrelative to the receiving part out of the locking position; andadjusting the angular position of the receiving part relative to thebone anchoring element.
 26. The method of claim 25, further comprisingadjusting the instrument to move the locking ring axially relative tothe receiving part to the locking position.
 27. A bone anchoring devicecomprising: a receiving part for coupling a rod to a bone anchoringelement, the receiving part comprising: a rod receiving portion having afirst end, a second end, a central axis extending between the first endand the second end, and a recess for receiving the rod, the recessextending from the first end towards the second end and forming two freelegs, the rod receiving portion further having an outer surface and afirst engagement structure defining a groove on the outer surface of therod receiving portion; and a head receiving portion at the second end ofthe rod receiving portion for accommodating a head of the bone anchoringelement, the head receiving portion having a free end and being flexiblefor inserting and clamping the head; and a locking ring configured to bearranged around the head receiving portion, the locking ring having anouter surface and a second engagement structure on the outer surface ofthe locking ring that extends farther radially outwardly than the outersurface of the rod receiving portion; wherein when the locking ring isaround the head receiving portion, the locking ring can assume a lockingposition where the locking ring exerts a force on the head receivingportion to lock an inserted head; and wherein the first engagementstructure and the second engagement structure are configured to beengaged by an instrument to move the locking ring relative to thereceiving part along the central axis from the locking position towardsthe first end of the rod receiving portion to a second position wherethe inserted head is pivotable and where the groove defined by the firstengagement structure is spaced apart axially from the locking ring andextends farther radially inwardly towards the central axis than all ofthe other parts of the outer surface of the rod receiving portion thatare located axially between the first end of the rod receiving portionand the locking ring.